This invention generally relates to deposition of thin films using ion beams and the like. Specifically, the invention has application to deposition of diamond-like carbon (DLC) films where requirements for the deposited films include low particle contamination and high uniformity.
Ion beam deposition of diamond-like films is known and has been studied by different authors. Enisherova et al in Material Science and Engineering B46 (1997), pp. 137-140, incorporated by reference here into, investigated properties of DLC deposited on a substrate using an industrial cold cathode ion source. Baldwin et al in U.S. Pat. No. 5,616,179, incorporated by reference here into, disclosed a DLC deposition method using an end-Hall ion source. Further, even though not particularly relevant to the present invention, to the extent it may be helpful background understanding of some other types of processing can be obtained from other publications, such as U.S. Pat. Nos. 5,427,669, 5,535,906, 5,645,698, 5,718,813, and 5,747,935, each to the assignee of the present invention.
Computer hard disk protective coatings and some other applications are sensitive to particle contamination of the surface. Those skilled in the art know that particle contamination problems can accompany virtually all carbon-containing plasma applications. Carbon material in such plasmas can tend to conglomerate into particles that are precipitated or formed on most, if not all, surfaces in the vacuum chamber, including the substrate surface. The particles often grow in size with time and, as mentioned, can find their way to the substrate surface. In addition, accumulated carbon material inside the ion source can change discharge parameters and eventually may short circuit ion source electrodes. While this may be tolerable in some applications, in sensitive applicationsxe2x80x94such as the computer disk processing mentioned abovexe2x80x94particulate or carbon contamination is not acceptable.
This can create a necessity to open the vacuum chamber on regular basis and to remove carbon deposits from the ion source and vacuum chamber wall. This maintenance can increase the downtime and may result in lost productivity. It may also create variability in processing. In such applications, the present invention can act to virtually eliminate particle contamination without the need to open the vacuum chamber for cleaning. In addition to producing particle-free films, an additional benefit of the invention can be the possibility of virtually maintenance-free operation of the ion source itself.
One additional desire well known to those skilled in the art is the uniformity of coating over the substrate surface. This aspect is especially difficult in systems that process one substrate at a time because it can be difficult to achieve particle free coating and even uniform distribution of ion beams current density and gas pressure over the substrate surface. As to the latter aspect, a conventional way to achieve high uniformity can be to move the substrate in front of the deposition source. This movement is often present in in-line and carousel type coating systems but in single substrate systems the movement of substrate can complicate the process significantly and increase the cost of equipment. Many times a complicated two-axis planetary pattern of substrate movement needs to be used, as in the paper of Enisherova, mentioned above.
Further, there is currently a desire in the disk industry to find a replacement for currently used magnetron-based amorphous carbon deposition systems. Such a replacement would preferably deposit diamond-like-carbon and fit into existing equipment. It would also not allow or require substrate movement during the deposition process. The present invention achieves high uniformity and particle free coating with stationary substrate by optimization of the ion source design and utilization.
Perhaps surprisingly, the present invention provides solutions to many problems in manners using technologies which others might have had available. However, the fact that there was a long felt but unsatisfied need for this type of invention while the needed implementing arts and elements had long been available and the fact that there was no full appreciation of the nature of the problem by those skilled in the art each seem to show how the invention is considerably more significant than simply a choice in mode of operation or the like for these applications. The significant inconvenience suffered by operators and the potentially substantial attempts by those skilled in the art to overcome the problems show the difficulties extant. Thus it appears that at least some of these difficulties were because of a failure to understand the problems to the degree now explained. Through adoption of other, less economical solutions and the large degree of improvement (rather than merely gradual steps), the invention may be shown to present approaches which others acted to teach away from. It may also indicate that the results of the invention would be considered unexpected if initially viewed without the hindsight of an exposure to this disclosure.
A method that is the subject of one embodiment of the present invention can make use of the fact that some cold cathode ion sources, such as the well-known multicell ion sources and linear ion sources series manufactured by Advanced Energy Industries, Inc., Fort Collins, Colo., are capable of running a discharge in an oxygen-containing gas mixture or in pure oxygen. The present inventors have found that a discharge can clean the ion source and vacuum chamber surfaces from carbon and that periodical application of a new mode of operation described herein, the reactive cleaning cycle, can allow the deposition process to run without adding any substantial particle contamination on the substrate. This may even exist virtually indefinitely. The discharge reactive cleaning cycle can also eliminate the need for opening the vacuum chamber in order to remove carbon or the like from the inside of the chamber and the ion source. Perhaps surprisingly, in some situations it may be that the reactive cleaning cycle time can be much shorter that the deposition time.
Additionally, those skilled in the art also know that it is difficult to achieve uniformity of the coating thickness over the entire substrate surface when substrates are coated one at a time by a wide ion beam, like in many hard disk coating machines. In the apparatus used by Enisherova et al, the substrate was moved in front of the ion source in a complicated planetary way during the deposition to make the film more uniform. For many applications, like hard disk protective coating, the substrate movement is not practical or is prohibitively expensive. Therefore, there is a need to achieve acceptable thickness uniformity with a stationary substrate. Accordingly, in other embodiments, the present invention discloses ways to optimize the apparatus design to achieve maximum uniformity at given maximum ion source size.
Accordingly, it is an object of the invention to avoid or minimize the effects of carbon or particle contamination in sensitive coating processes. In keeping with this object it is a goal to provide a system which acts automatically and thus without a need to have an operator physically access the interior of the chamber to address an undesirable condition.
In is also an object to provide coatings of higher quality and of more uniformity than was previously done.
Yet another object is to provide a new mode of operation of an ion source so that different types of processing may be accomplished in a variety of contexts.
Naturally, other objects of the invention are disclosed throughout other areas of the specification and claims. In addition, the goals and objectives may apply either in dependent or independent fashion to a variety of other goals and objectives in a variety of embodiments.